Yeah, that same problem bit me in the butt big-time with a customer.
If you look at the orders, you'll probably see gaps in the sequence numbers. These will account for
the "missing" charges/orders.
I had to use the wget option in order for the problem to completely go away. Setting RPC mode ended
up taking down my server.
AFAICT, the authorizenet module -should- be using wget by default, since it works 100% of the time.
Whatever they are currently using often breaks. Stuff like this gives IC a black eye.
Bob